1. Field of Invention
This invention pertains to the art of methods and apparatuses for providing electrical conductors encompassed by a layer of fiberglass to provide high temperature operating capability, and more specifically to methods and apparatuses for providing insulated electrical conductors for which the fiberglass, in close proximity to the conductor, is heat-treated to render the fiberglass sufficiently frangible to enhance the strippability of the fiberglass.
2. Description of the Related Art
It is well known to use fiberglass in the fabrication of high temperature electrical wires and cables. Fiberglass is used to encase a conductor material, as an electrical insulation, because it can withstand high temperatures. Fiberglass has a softening point above 800xc2x0 C. Additionally, fiberglass is flexible and comes in the convenient forms of filaments, yarn strands, woven cloths, braided cloths, tapes, and sleeves.
It has also been the practice to impregnate fiberglass electrical insulation with high temperature binders, varnishes, and resins of various kinds and types improve electrical insulation properties and resistance to moisture. Characteristically, they tend to stiffen the insulated conductor or cable.
In some instances, high temperature resistant electrical insulation combine mica with fiberglass to provide resistance to temperatures of 450xc2x0 C. or higher. The mica may be bonded to the fiberglass by any means known to be of sound engineering judgment. For example, hard and non-plyable resinous compositions may be used to bond the mica to the fiberglass. U.S. Pat. No. 3,629,024, which is incorporated herein by reference, discloses the foregoing methods to incorporate mica into the fiberglass for high temperature applications.
It is thus obvious that numerous methods and apparatuses have been developed to produce electrical conductors that operate at high temperatures. And, as mentioned above, it is generally well known that fiberglass alone, or fiberglass in conjunction with other materials such as mica, has been used to produce insulation for high temperature wire products. However, high temperature electrical conductors utilizing fiberglass have an inherent difficulty in that the fiberglass may be difficult to strip away from the wire. Untreated fiberglass when stripped away, leaves filaments and rough edges.
Fiberglass is difficult to strip away from the electrical conductor because of its long, soft, fibrous nature. Additionally, tools used to strip layers of material away from the electrical conductor are typically sized so that they do not contact the conductor itself. This is commonly done so that the conductor itself is not crimped or damaged during the stripping process. Consequently, the fiberglass closest to the electrical conductor is not cut. This results in a time consuming process wherein these remaining fibers must be removed individually.
The fact that fiberglass is difficult to strip is a serious problem because frequently the conductor needs to be exposed by removing the protective layers which surround it. This is typically done so that lengths of the conductive wires or cables may be coupled together. Alternatively, the layers covering the electrical conductor may need to be stripped away so that the conductor may be attached to a particular device or power supply. Thus, fiberglass which is difficult to strip away from the electrical conductor creates a time consuming and expensive difficulty.
Thus, it would be desirable to have a high temperature electrical conductor encased in fiberglass that can be completely and easily stripped away from the conductor itself. The current invention provides fiberglass that can be used to create high temperature electrical conducting products, but which is sufficiently frangible so that it may be easily removed from the conductor. The current invention also provides a method to make this frangible fiberglass.
It should be noted, however, that an insulated conductor comprising an easily strippable fiberglass does exist in the related art. However, unlike the invention disclosed in the current application, the fiberglass in this known insulated conductor must be chemically treated before it may be easily removed from the conductor. This is disclosed in U.S. Pat. No. 5,468,915 (""915 patent), which is incorporated herein by reference.
The ""915 patent discloses that the fiberglass is treated with a chemical such as sodium silicate so that the fiberglass may be more easily removed from the conductor. As shown in FIGS. 2 and 4, the chemical reacts with the fiberglass, causing the fiberglass to become sufficiently frangible to break, and thus eliminating stringing when the fiberglass is stripped away from the conductor. Additionally, according to the ""915 patent, heat treating the chemically treated fiberglass accelerates the chemical reaction and causes the fiberglass to more quickly become sufficiently frangible.
As shown in FIG. 4 of the ""915 patent, the strands are passed through a pool of the sodium silicate prior to being disposed upon the conductor. Subsequently, further layers of fiberglass are wound onto these treated strands of fiberglass. The treated strands of fiberglass operate to transfer some of the sodium silicate solution to these outer layers. Finally, according to the ""915 patent, heating the insulated conductor at a temperature of about 600xc2x0 F. for about 1.5 minutes produces the most desirable results.
Consequently, after the chemically treated fiberglass of the insulated conductor, of the ""915 patent, is heat-treated, all of the layers of fiberglass may be easily stripped away from the conductor. With the foregoing combined chemical and heat treatments, the fiberglass is rendered sufficiently frangible so that it may be removed from the conductor without having the tendency to leave strands of fiberglass that need to be individually removed.
The current invention improves upon the ""915 patent in that it does not require the fiberglass to be chemically treated. Rather, the current invention produces frangible fiberglass that is easily removable from a conductor simply by heat treating the fiberglass layers.
Difficulties inherent in the related art are therefore overcome in a way that is simple and efficient while providing better and more advantageous results.
In accordance with one aspect of the current invention, the electrical conductor is wrapped with fiberglass and then heated to the devitrification temperature of the fiberglass.
In accordance with another aspect of the present invention, the fiberglass wrapped electrical conductor is not chemically treated.
Yet another aspect of the current invention includes a method of producing heat-treated fiberglass wrapped electrical conductor.
One advantage of the present invention is that it is easy to manufacture and can be made economically.
Another advantage of the present invention is that an electrical conductor, capable of operating at high temperatures, is produced wherein the layers on the conductor may be easily removed therefrom.
Yet another advantage of the current invention is that frangible fiberglass can be produced with fewer materials and using fewer procedures.
Another advantage of the current invention is the frangible fiberglass layer heat set around the conductor allowing for immediate application of insulation enhancing coatings and or binding agents.
An unexpected advantage that wire made with a heat set glass layer exhibits is dramatically reduced glass fly and dust that normally results during the insulation removal process necessary to terminate wire.
Another unexpected advantage of the current invention is a 100% to 150% increase in insulation strength as measured by insulation resistance testing at 900xc2x0 F. over wire manufactured by the process in the ""915 patent.
Another advantage of the current invention is a 200% to 300% improvement in current leakage performance at 90% relative humidity as compared to wire manufactured by the process in the ""915 patent.
Still other benefits and advantages of the invention will become apparent to those skilled in the art to which it pertains upon a reading and understanding of the following detailed specification.